Critical-speed control



July 17, 1928.

C. R. SESSIQNS CRITICAL SPEED CONTROL Filed May 29, 1922 INVENTOR n v O Patented July 17, 1928.

PATE CRITICAL-SPEED CONTROL.

, Application filed May 29,

This-invention relates to a construction affording means to control the frequency of' a vibration, or'whirling, of a revolving shaft so that the'speed of revolution may notcoincide or 'be unfavorably near coincldlng -with a whirling or critical speed of the Another obiect 'of this invention is to pro-' duce a construction lessening or eliminating vibration and thesevere strain due to critical A furtherobject of the invention is to produce a construction adapted to'high speed.

Other objects of the invention will appear as the description proceeds. An embodiment" Fig. I isa view ofa shaft carried in two or more bearings with means of adjusting the position of these hearings in the direction i so ' apulley 9, the shaft 1 being rotatably jourforth. Between the critical'speeds of the of the axis of the shaft.

Fig. IIshows afixed bearing;

' Fig. III shows a free bearing. V

Fig. IV illustrates a large bore hearing. In detail, the construction illustrated in the drawings comprises ashaft 1 adapted; to

be rotated by afdrive belt8 passing around naled at its opposite ends in fixed bearings 2 and 3. The type of fixed bearing utilized is shown in Fig. II. The use 'of 'a" relatively long flexible j'shaft 1 for deep well pump" work, without providing any intermediate,

bearings on, said shaft, has'disclos'ed that such a shaft fwill have numerous critical speeds, depending upon the shaft length, di-

ameter, revolving speed, axial stress, and so shaft, there arespeedsat which the shaft Will not vibratefandfat which, if it is forcibly deflected, said shaft'willgpositively return to a quiet condition, a condition of operation that. is to be desired 1 In order to keep the shaftin' a quiet running condition at all times, my invention contemplates the plac- W, ing of athirdbearing at or near one of the. "no two fixed bearings, 2 or .3, so that the third bearing can bemoved or adjusted relative to the otherbearings to effectively shorten the shaft length. In Fig. I, .I have shown a bearing 6, a detail of whichis shown m'Fig. I11, arranged the-fixed bearing 2.

greater detail.

great lateral. deflection is a.

1922. Serial No. 564,665.

length, actually such a condition doesnot take place, because the shaft in all cases is a definite piece of'material of 'fixed length,

but the effective length of the shaft between After'the third or adjustable bearing 6has' been regulated to operating conditions, the fixed bearing 2 could be removed from'the construction, and not interfere'with the efficiency of'operation of the shaft1;"'However, the fixed bearing 2 would neverbe' omitted from the construction,-'because, al-

though the'length of the shaft 1 'can'be calculated to cope with the conditions under .which it is to be operated, nevertheless, op-

erating conditions may change or vary, and

hence the movable bearing 6 can be alteredv accordingly to meet and function with the new conditions of operation. A pair of bearings 4 and 5, a detail of which is shown in;

Fig. IV, are interposed between the movable bearing 6 and the fixed bearing 3. The large bore control bearings 4 and -5 prevent great lateral deflection of the shaft at critical speed. The operation of these large bore bearings will be hereinafter explained in Bearings 4,15, 6 etc. are'slidably held on a frame or colu1nn10 and a re movedin' the direction of the axis of the shaft by a screw 11 turning in a thread 12 in the bodyqof the bearings. The screw 11 has a portion 13 fitting in a recessl in the body'of'the bearing ,2 to take the thrust. The pitch of the threads 12 in bearings-5 and 6 may be respectively two and four times that in bearing 4150 that equal distances between bearings'may be maintained. The screw 11 may be operated manually by a crank 1 5 or may m 0mm CHARLES ROBERT SESSIONS, or sen rnAnCrsco, CALIFORNIA, Assronon or one,

: HALF TO JOHN A. DENT, or LAWRENCE, KANSAS.

though I speak of shortening the shaft hearing 3 and the movable bearing be operated by' a gear 16-17 driven by motor 18 actuated 'suitable' electric curby suitable thrust bearings forming part,

for example, of bearings 2 and 3; This 'stress may be varied by weightin thegcase of a' vertical shaft and generally by the movement of bearing-2 relatively to the bearing 3 and in the direction of the axisr-of'the shaft.

In long shafts, in starting and stoppinig,

ical speed by placing, at suitable inter-ma,

V di'ate points, large bore control bearings as shown in Fig. IV. The bore of these bearlngs is largeso that atnormalrunning the shaft docs not touch the: bearing surface but at critical or whirling speeds the shaft rolls and rubs on the bearing surface and is restrained against extreme deflect-ion.

I am aware that a revolvingshaft, deending on its diameter, length, nature of oading, character of bearing support,'axial and torsional stress, and coeflicient of elasticity. will have one or more critical or whirling speeds,speeds of revolution at which the periodic disturbing force of unbfilanfcefhas thefre uency of natural vibration and'at whic theshaft whirls,

,or the speed at which the'elast-ic resistance ofthe shaftto lateral deflectionis overcome by the centrifugal force of unbalance. Therefore a vibrating shaft may be quieted orma'de to run smoothly by varying its -length between-bearings or itskaxial stress that its critical or whirling, speed would occur ata speed of revolution conveniently remote from the operating speed. Axial. stress may :be difficult to predetermine in design and may vary in operat1on. In such a case the-shaft length between bearings may be varied to suit and to cause the operating speed to be favorably non-coincident with a critical or whirling speed. If the'bearing length is fixed by constructionit may be 'convenient'to vary the. axial stress to ob- .tainquiet running. a

- My calculations 'show that a vertical steel shaft, offlan inch in'diameter-100 feet ing 6 approximately long between top change the vibrating condition of the to that of the next critical condition below the sixty first critical tionsper minute, 150 pounds, and transmittlng a torsional stress of 5 h'0rse' power, will be vibrating at approximatelyits sixty first critical speed. A change of 18 inchesin the effective shaft length, caused by moving the movable-bear shaft 1, away from'the fixed bearing 2, will shaft speed. A change in the effective shaft length ofabout 9 inches would correspond to a condition of no. vibration,

55.. I shaft would'vibrate critically the sixtyfirst -time if the shaft were revolved under the being the quiet condition of operation to be desired. The sixty first criticalspeed, above referred to, means thatspeed at which the conditions; already mentioned from .rest,

' cal speed. The sixty progressively, up to I minute and passing through thefirst, third, fifthand so forth, up to the sixty first critifirst critical; speed,

above referred to, means that-speed of revolution synchronizingor resonant with the, shaft, (a funda-.

vibrating periods of :the

and bottom'bearings, re- -volvingiat a constant speedof 5,000 revoluwith an axial tension of 18 inches down on the.

5,000 revolutions per I efficient or inefiicient operating condition of z the shaft.

A vertical shaft has been used-for illustration but my invention is not" changed if the shaft is-horizontallyisupported or -may -have concentrated or lateral 'loading as shown by dotted lines in Fig. I. My invention is equally applicable tola" shaft'having two, three, or more bearings. .WVhat I claim is as follows, modifications may be made in thercons'truction shown in the .dr'a-wingsand above described formavithin the purview oflmy invention 1. In combination,- fixed bearings; a driv-" en shaft having its opposite endsj'ournaled in sald bearings; and-means, ad acentone of-said bearings. adjustable axially relative thereto'to control the frequency' o-f vibration of said shaft at various critical speeds- V 2. An apparatus to control the frequency of vibration of'a drivenshaft comprised of abearingarrangedadjacentan end of the shaft in proximate contact therewith; and means to move the bearing axially relative to said shaft 'as thecritical -speed of the shaft varies. 1 .f

An apparatus to-control thefrequency ofv-ibration of? a driven, shaft comprised of, fixed bearings' having the opposite ends of thesh'aft journale'd'therein, and a movable bearing arranged'between the fixed bearings; and means to vary the .distancebetween the regulate the whirling speed .of the shaft and control the frequency of vibration atany critical speed. I a 7 4. An apparatus such as described comprising in'combination, fixed shaft bearings; a' shaft journaled in said beaings; aphirality of free bearings-intermediate said fixed bearingsand having said shaft confined therein; .and means on said. fixed-bearings T connectedto said free bearings for adjusting said free bearingsaxially relative to sai fixed bearings when said shaft is revolving near itscriticalwhirling speedfor controllingthelateraldefiection of said shaft.

5. In, combinationawith a rotatable shaft journaledgin fixed-bearings, of zmeans for controlling-the whirlingfspeecl of said shaft,

comprising,- adjustable free bearings. intermediate said fixed bearings, and means-for varying the distance between the free and fixed bearlngs relative .to said revolving but I various" movable bearing and the fixed bearings to shaft to compensate for variations in axial stress.

'6. An apparatus to control the vibration of a rotating shaft at various critical speeds, comprised of a shaft journaled at its opposite ends in fixed bearings; means to rotate said shaft; and a bearing adjacent an end of said shaft adjustable axially thereon rela tive to one of the fixed bearings.

7. An apparatus to control the Vibration 0f 10 a rotating shaft at various critical speeds, comprised of a, shaft journaled at itsopposite ends in fixed bearings; means, to rotate said shaft; a bearing adjacent an end of said shaft adjustable axially thereon relative It to one of the fixed bearings; and means to adjust the last mentioned bearin axially.

CHARLES ROBERT S SSI ONS. 

